Digital models of the earth are usually derived using some sort of visual data source, images forming stereo pairs, or LIDAR. Visual approaches of terrain extraction produce the visible surface. This visible surface may include some parts of the ground surface as well as other features or artifacts such as buildings, vehicles, vegetation, etc. These models are called digital surface models (“DSM”).
However, in some examples the visible surface may not be desired. For example, it may be important to have a model or map of an area that does not include artifacts such as those listed above, but rather, the elevation of the bare earth. This type of model is called a digital terrain model (“DTM”).
Generating a DTM from a DSM can be challenging. It requires removing artifacts from a DSM and interpolating the elevation of the earth without those artifacts. Various systems attempt to remove these artifacts automatically. For example, some systems may remove buildings by specifying the terrain elevation of the surrounding land (for example, using a typical flood filler algorithm) and removing or interpolating (for example, using a hole-filler algorithm) values above that elevation. However, that approach assumes that the surrounding land is flat and will be less useful on sloped terrain.